Phthalocyanine compounds are useful as coatings, printing inks, catalysts or electronic materials. In recent years, they have been extensively studied particularly for their use as electrophotographic photoreceptor materials, optical recording materials and photoelectric conversion materials.
In the field of electrophotographic photoreceptors, there has recently been an increasing demand to develop an organic photoconductive material having its photosensitive wavelength region extended to a longer side of near infrared light (780 to 830 nm) which corresponds to a wavelength region of a semiconductor laser so that it can be applied to a digital recording system, such as a laser printer. Known photoconductive materials for semiconductor lasers so far proposed from this viewpoint include squarylium compounds as disclosed in JP-A-49-105536, triphenylamine type tris-azo compounds as disclosed in JP-A-61-151659, and phthalocyanine compounds as disclosed in JP-A-48-34189 and JP-A-57-148745 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
In cases where an organic photoconductive material is used as a photosensitive material for semiconductor lasers, it is required to have a photosensitive wavelength region extended to a longer side and to provide a photoreceptor having satisfactory sensitivity and durability. None of the above-described conventional organic photoconductive materials sufficiently satisfies these requirements.
In an attempt to overcome the drawbacks of the conventional organic photoconductive materials, the relationship between their crystal form and electrophotographic characteristics has been studied. In particular, many reports have hitherto been made on phthalocyanine compounds.
It is known that phthalocyanine compounds generally exhibit several different crystal forms depending on the process of production or the process of treatment and that the difference in crystal form has a great influence on their photoelectric conversion characteristics. For example, known crystal forms of copper phthalocyanine compounds include .alpha.-, .pi.-, .chi.-, .rho.-, .gamma.-, and .delta.-forms as well as a stable .beta.-form. These crystal forms are known capable of interconversion by a mechanical strain, a sulfuric acid treatment, an organic solvent treatment, a heat treatment, and the like as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. Further, JP-A-50-38543 refers to the relationship between a crystal form of copper phthalocyanine and its electrophotographic characteristics.
Phthalocyanine crystals having any desired crystal form have generally been prepared by treating phthalocyanine having been subjected to acid pasting or mechanical grinding with an appropriate solvent. Special treatments for improving their electrophotographic characteristics have been reported. For example, JP-A-61-171771 discloses purification of phthalocyanine crystals by treatment with N-methylpyrrolidone for improvement in electrophotographic characteristics. Influences of impurities on electrophotographic characteristics have also been reported. For example, DENSHISHASHIN GAKKAISHI, Vol. 28, No. 3, p. 269 (1989) describes that repetition of purification by sublimation brings about great changes of electrophotographic characteristics with the structure and crystal form being equal. With reference to hydroxygallium phthalocyanine crystals, JP-A-1-221459 refers to the relationship between the crystal form and electrophotographic characteristics with respect to the crystals obtained by acid pasting only.
However, any of the phthalocyanine compounds proposed to date, inclusive of the above-mentioned hydroxygallium phthalocyanine crystals, is still unsatisfactory in photosensitivity and durability when used as a photosensitive material. Even when the above-mentioned special process for production or treatment may be followed, satisfactory photosensitivity and durability as a photosensitive material has not yet been reached. It has thus been demanded to develop a new phthalocyanine crystal with improved photosensitivity and improved durability while retaining characteristics of phthalocyanine compounds.